A wide variety of methods for manufacturing resin coated sand for a shell mold is available, and in general, a hot marling method is employed in terms of productivity and quality, i.e., the resin coated sand is manufactured by melting heated new sand or recycled sand and a phenolic resin followed by adding an aqueous solution of hexamethylenetetramine which is a curing agent. The resulting RCS is injected into a predetermined die assembly, and used as the casting mold by curing the phenolic resin.
By the way, aluminium parts have been often used recently for the purpose of lightening the parts related to automobiles, and increased castings of aluminium alloys having a low pouring temperature (about 700° C.) have been produced. When the casting is produced using the aluminium alloy having a low melting temperature, it becomes difficult to decompose and deteriorate the resin, and the casting mold itself does not crumble and remains in the casting after solidifying the metal in the conventional casting mold using the phenolic resin.
As measures for this, a method of treating again the casting with heat after casting in a high temperature furnace to remove the remaining casting mold, and a method of giving a physical impact to the casting to remove the casting mold are available. However, both the methods require considerable energy, and a secondary load is given to a casting product, which are problematic. As the method for improving them, for example, the method of using phosphate esters as a crumbling agent (see patent Document 1) is proposed.
Patent Document 1: Japanese Patent Application Laid-Open No. 58-3745